1. Field of the Invention
The present invention generally relates to processes for making synthetic smectites. More particularly, this invention relates to processes for making a variety of synthetic smectites, including but not limited to synthetic smectites having a variety of charges, sizes, and/or morphologies.
2. Description of the Related Art
Most clay minerals, as found naturally, may be in an impure state and the complete purification of some may be difficult and expensive. Further, there may be situations in which the supply of a clay mineral of a particular chemical composition, either pure or impure, may be insufficient. Thus, it may be desirable to manufacture synthetic clay-like materials in substantially purer forms and/or in more commercially economic yields. Additionally, it may be desirable to manufacture greater quantities of more pure clay-like materials.
It may also be of interest to manufacture synthetic clay-like materials having properties similar to or better than naturally occurring clays. Such improved properties may include improved rheological control, purity, crystallinity, and morphology. Examples of applications in which synthetic clay-like materials with improved properties may be used include, but are not limited to coatings, inks, greases, personal-care products, home-care products, nanocomposites, drilling fluids, pharmaceuticals, catalysis, purification methodologies, or ion-exchange applications.
Different classes of smectites may be synthesized. In synthesized smectites, some of the silicon, aluminum, magnesium, or other ions may be replaced by other ions of different charges. As a result of these substitutions, the structure may acquire a negative charge, which may be neutralized by associated exchangeable cations such as alkali metal cations. Therefore, smectite clay minerals of many different compositions may be made by introducing into the reaction mixture ions desired in the composition. In addition to these elements, sufficient alkali metal compound, in the form of the carbonate or hydroxide may be added, to maintain the solution at the desired alkaline pH throughout the synthesis. The precipitate may then be further processed by filtering, washing, or drying. Additional information pertaining to synthesis of smectites may be found in U.S. Pat. No. 3,586,478 and U.S. Pat. No. 3,671,190 to Neumann, both of which are incorporated herein by reference. U.S. Pat. No. 3,666,407 to Orlemann, which is incorporated herein by reference, describes a method of producing hectorite by calcining a mixture of talc and lithium carbonate followed by subsequent mixing of the calcined material with a sodium silicate and sodium carbonate. The mixture was then hydrothermally treated. U.S. Pat. No. 3,892,655 to Hickson, which is incorporated herein by reference, describes a method of preparing a layer-type, trioctahedral, clay-like material. The layer-type material is prepared by hydrothermal crystallization from aqueous slurries of a mixture of hydrous silica, hydrous alumina, hydrous magnesia and fluoride. The pH is adjusted from about 7 to 10.5 and the slurry is then heated to a temperature of from 550° F. to 700° F. The slurry is stirred under pressure for about 0.5 to 4 hours. U.S. Pat. No. 5,393,411 to Holmgren, which is incorporated herein by reference, describes the preparation of a fluorided beidellite clay. The process reacts a mixture containing reactive sources of aluminum, silicon, a cation salt and a fluoride source. The reaction is carried out a pH of about 4 to 9 at a temperature of about 150° C. to about 300° C.
Current methods may not provide synthetic clay materials with sufficient homogeneity with regard to metal cation ratio, morphological features, and/or reduction of impurities, under commercially economic conditions. Therefore, it may be desirable to provide control over the morphology, size, crystallinity, and/or charge of certain synthetic smectites. It may be desirable to economically produce a material that exhibits improved performance in various applications.